The invention relates to a process and apparatus for clarifying photofinishing chemical effluent, in particular the liquid effluent produced from "mini-labs" using automated photofinishing machines operated by relatively unskilled personnel, as opposed to larger, high production photofinishing chemical laboratories staffed by skilled technicians.
In the past, photofinishing chemical laboratories for processing relatively large volumes of colour photographs were relatively large organizations staffed by skilled personnel, and were accustomed to dealing with relatively large quantities of liquid waste generated in high volume production photofinishing operations. In large organizations, processing of the photofinishing chemical effluent could be economically handled by relatively high capacity and costly effluent filtration equipment, and the large quantities of liquid waste that was processed generated relatively large quantities of toxic concentrates which could be disposed of economically.
In the last few years, automated photofinishing equipment has become widely available and is used in small "mini-labs" which are known for fast service, and can commonly produce prints from a negative film within one hour of the customer leaving the film for processing. Automated photofinishing apparatus permits the use of a relatively small number of operators, and because many of the technical operations are performed automatically by the apparatus, the level of skill of the operators is considerably less than is required in the earlier large processing labs. In the last few years there has been a large increase in "mini-labs" which are distributed throughout urban areas, and each "mini-lab" generates photofinishing chemical effluent. Common practice is to dump this effluent into municipal sewers, which produces corresponding problems downstream in a sewerage plant, if one is provided, or in the body of water receiving the sewer discharge. When the number of "mini-labs" is relatively small, the accumulative effect of photofinishing chemical discharge is relatively minor, but as the number of "mini-labs" increases, the accumulative effect becomes a serious consideration, and municipalities are now requiring treatment of these discharges, even of the relatively small amounts from "mini-labs".
In relatively large photofinishing laboratories, photofinishing chemical effluent is sometimes purified by evaporation and distillation. The distillation produces a distillate which is sufficiently pure to dump into the sewer, and the remaining toxic concentrate can be incinerated or sent to a hazardous waste landfill.
Because of the shortage of skilled personnel in the "mini-labs" and the relatively small quantities of effluent produced, processing the effluent from "mini-labs" using conventional techniques found in the larger labs is not economic, or practical. Due to transportation costs, and the hazards of transporting toxic wastes, it is also not practical to have regular pick-up of untreated photofinishing chemical effluent by toxic waste trucks, for processing in a larger central facility.
To the inventor's knowledge, attempts to use membrane filtration techniques for purification of photofinishing chemical effluents have been unsuccessful because the effluents are highly contaminated or concentrated liquids with complex chemicals which quickly plug the fine pores of the membranes, reducing life of the membranes which are costly. In addition, even if the plugging of the membrane could somehow be avoided, the high concentration of chemicals in the effluent causes concentration polarization at the membrane surface, and chemical interaction between the effluent and the membranes which renders membrane filtration by itself unpractical for photofinishing effluent.
What is required for "mini-labs" is a photofinishing chemical effluent treatment system which requires minimal intervention by skilled or unskilled operators, and permits processing of liquid effluent so that final liquid discharge is of an acceptable quality for dumping in municipal sewers. In addition, any toxic materials in the effluent should be concentrated so as to be in relatively small volumes to permit economic transportation of the concentrate to a central processing plant for further processing or disposal. To the inventor's knowledge, there are no suitable compact, low-cost "user-friendly" photofinishing chemical effluent treatment systems available for "mini-labs" as described above.